If your CO alarm is sounding RIGHT NOW:
Get everyone out immediately. Leave the door open. Call 999. Do NOT re-enter under any circumstances.
National Gas Emergency Service: 0800 111 999
Carbon Monoxide Detectors in London -- Legal Requirements, Best Alarms and Where to Place Them
CO is odourless and colourless -- you cannot detect it without an alarm. Around 40 people die from accidental CO poisoning in the UK every year, and hundreds more are hospitalised. This guide covers what the law requires in London, where to position your detectors, and which alarms to buy.
Legal Requirements
Is a CO Detector Required by Law in London?
Landlords (since October 2022)
LEGALLY REQUIREDThe Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 require all landlords in England to install a CO alarm in every room with a gas appliance (boiler, gas fire, gas hob) or solid fuel appliance. Local authorities can issue improvement notices and levy fines of up to £5,000 for non-compliance.
Homeowners
STRONGLY RECOMMENDEDNo legal requirement for owner-occupiers, but the NHS, Fire Service and Gas Safe Register all strongly recommend one. CO alarms cost as little as £15 and save lives. Given that 40 people die from accidental CO poisoning in the UK each year, the risk-to-cost ratio is clear.
New builds
LEGALLY REQUIREDBuilding regulations (Approved Document J) require a CO detector wherever a combustion appliance is present in a new build or extension. This applies to gas boilers, gas fires, solid fuel stoves, and oil boilers.
HMOs (Houses in Multiple Occupation)
LEGALLY REQUIREDCO alarms are required in every habitable room containing a gas appliance. Interconnected alarms (such as the Aico Ei208W) are typically required so all alarms sound if one detects CO -- a single alarm in a bedsit may not be heard in another room.
London Borough enforcement
LOCAL AUTHORITYLondon's 32 borough councils enforce the regulations. Environmental health officers can inspect properties and issue improvement notices. Councils including Camden, Hackney, Tower Hamlets and Southwark have run active enforcement campaigns.
Risk Awareness
6 Common Sources of Carbon Monoxide in London Homes
CO is produced by any fuel-burning appliance when there is incomplete combustion -- not enough oxygen to convert all carbon to CO2. These are the six most common sources in London properties.
Faulty boiler
Incomplete combustion releases CO instead of CO2. The most common domestic source of CO poisoning. An annual Gas Safe service significantly reduces the risk -- the engineer measures CO and CO2 levels in the flue gas directly.
Blocked flue
CO cannot escape outside and accumulates inside the property. Caused by birds' nests, debris, or damaged flue lining. Particularly common after storms or in properties where the flue has not been inspected for several years.
Gas hob
A yellow or orange flame (instead of blue) indicates incomplete combustion. Keeping burners clean reduces risk. Hobs produce lower CO concentrations than boilers but can still be dangerous in poorly ventilated kitchens.
Gas fires (decorative)
Often poorly ventilated and very high risk if the flue is blocked. Decorative gas fires were frequently fitted in London Victorian fireplaces without adequate chimney inspection. Get checked annually by a Gas Safe engineer.
Running engines in an attached garage
Car exhaust, generators, and lawnmowers produce large volumes of CO. A garage attached to the house allows fumes to seep directly into living spaces within minutes. Never run an engine in an attached or integral garage.
Neighbours' shared flue or chimney
In terraced houses and purpose-built flats, chimney stacks are often shared between properties. A blockage in a neighbour's section can cause your neighbour's CO-laden exhaust to back-draft into your property. More common in older London conversions.
Placement Guide
Where to Put a CO Detector in Your Home
Do place here
Room with boiler
Within 1-3 metres of the boiler at head height. This is the highest priority location in any home.
Room with gas fire
Within 1-3 metres, at head height. Especially important for decorative gas fires in fireplaces.
Bedroom (if boiler is on same floor)
Position between you and the appliance. You need to wake you if CO accumulates while you sleep.
Loft (if boiler is in loft)
Essential. A loft boiler fault can flood the loft with CO and it may enter the house slowly -- easily missed.
Do NOT place here
Kitchen (above or near hob)
Cooking produces small amounts of CO and steam that will trigger constant false alarms, teaching residents to ignore the alarm.
Directly above the appliance
CO is roughly the same weight as air and disperses through the room. Directly above gives no advantage and risks heat damage.
In a draft or near a window
Air currents dilute CO before it reaches the sensor, reducing sensitivity. Keep away from windows, doors, and extractor fans.
In a cupboard or enclosed space
Air circulation is needed for the sensor to sample room air. Never enclose the detector.
Buyer's Guide
Best CO Detectors for London 2026
Always look for EN50291 certification on the packaging -- this is the UK and European standard for CO detectors. An uncertified alarm may not meet accuracy or alarm threshold requirements.
| Detector | Type | Price | Certification | Notes |
|---|---|---|---|---|
| Kidde 7CO | Standalone | £15-£25 | EN50291 | Reliable, 7-year electrochemical sensor. Widely available. |
| Deta S0818 | Standalone | £15-£20 | EN50291 | Good value. Common choice for London rental compliance. |
| Google Nest Protect | Combined smoke + CO | £90-£110 | EN50291 | Smart app alerts, links with Nest thermostat. Best for owner-occupiers. |
| Aico Ei208W | Wireless interlink | £40-£60 | EN50291 | Interconnects multiple detectors so all sound when one triggers. Required in HMOs. |
Prices correct June 2026. EN50291 is the mandatory UK/EU certification standard -- check packaging before buying.
Emergency Protocol
What to Do If Your CO Alarm Sounds -- 5 Steps
Do NOT investigate
Do not look for the source. Do not try to find the faulty appliance. CO poisoning disorients you fast -- you may lose the ability to act within minutes of exposure.
Get everyone out immediately
Leave via the quickest exit. Take pets with you. Leave all doors open as you exit -- this ventilates the property and helps disperse CO.
Call 999 once outside
Inform the operator that your CO alarm has sounded. Emergency services will attend to confirm CO levels and make the property safe.
Call National Gas Emergency: 0800 111 999
If a gas appliance is the source, the National Gas Emergency Service will attend to isolate the gas supply and make it safe.
Do not re-enter until declared safe
Emergency services will use CO monitors to confirm the property is safe before allowing re-entry. After the incident, all gas appliances must be inspected and signed off by a Gas Safe registered engineer before you use them again.
Prevention
Annual Boiler Service is Your Best CO Safeguard
A Gas Safe boiler service includes a combustion analysis: the engineer directly measures CO and CO2 concentrations in the flue gases using a calibrated analyser. This catches incomplete combustion -- the main cause of CO poisoning -- before it becomes dangerous.
Engineer checks CO and CO2 levels in the flue gas with a calibrated analyser
Flue, heat exchanger and burner inspected for cracks or blockages
Gas pressure verified against manufacturer specification
Identifies conditions that lead to CO release before they become dangerous
Cost Guide
CO Detector and Boiler Service Costs in London 2026
All prices include VAT. Detector prices are retail averages; fitting costs apply to landlord compliance visits. Boiler repair costs are illustrative ranges -- exact quote given before work starts.
CO Safety Questions
Frequently Asked Questions
Worried About CO Risk From Your Boiler?
An annual boiler service includes combustion analysis -- the engineer measures CO levels in the flue gas directly. Most CO risks are caught and fixed in a single service visit. Call us to book a Gas Safe engineer in London today.
Gas Safe registered · No call-out fee on jobs over 2 hours · 24/7 London